Project Summary: Overconsumption of food and reduced physical activity cause obesity, but limited understanding of the neuronal circuits regulating these behaviors has hindered development of therapies. Since the lateral hypothalamic area (LHA) of the brain controls the motivation to ingest and move it has been studied for potential to support weight loss, but most LHA neurons promote ingestion and weight gain. In contrast, during the last funding period we identified LHA neurons expressing the neuropeptide neurotensin (Nts) that restrain feeding and promote energy expenditure to decrease weight. Curiously, activating LHA Nts neurons also invokes a burst of water intake that acutely causes weight gain, but once drinking normalizes then feeding suppression and increased energy expenditure lead to weight loss. Taken together, these data suggest that preventing dipsic behavior and biasing specifically for LHA Nts-mediated feeding restraint and physical activity might improve the degree of weight loss. This could be possible, based on our preliminary data that LHA Nts neurons densely project to two separate sites in the brain that are implicated in the control of drinking and feeding, respectively. These data led to the central hypothesis of this renewal application: LHA Nts neurons coordinate feeding suppression and drinking via the VTA and LPO, respectively, which requires signaling via neurotensin receptor-1 (NtsR1). To investigate this we will use tract tracers and in vivo calcium imaging to define the specific LHA cells and circuits that organize feeding vs. drinking, and hence precise neural targets to mediate weight loss behaviors (Aim 1). To define the functions of Nts projections to the VTA vs. the LPO we will optogenetically stimulate LHA Nts terminals in each site, thereby revealing if there are dedicated circuits sufficient to direct feeding vs. drinking (Aim 2). We will then define the necessity of Nts signaling via NtsR1 in the VTA or LPO for energy balance, and the ability of these NtsR1 neurons to mediate weight loss without adverse effects (Aim 3). Taken together, these studies will define the circuits, signals and behaviors by which LHA Nts neurons mediate weight loss, suggesting where and how to target future pharmacological therapies to treat obesity.